Drywall & Plasterboard Calculator
Find how many sheets of drywall (plasterboard) to buy for a room, with the tape, joint compound and screws. Advanced adds more rooms and walls, sheet layout, corner bead and cost.
Type feet and inches like 12'6" in any box. Takes away one door and one window of a typical size. Advanced lets you change them.
Across (horizontal) is common on walls up to about 8 ft. This changes the joints to tape and the drawing.
Ceilings often use longer or sag-resistant boards.
10% is usual. 12–15% for many corners and openings.
Typical: about 14 lb of ready-mixed compound per 100 sq ft (0.7 kg/m²) for tape and two more coats; a 4.5 gal bucket is about 62 lb. Screws: blank uses about 1 per sq ft on walls and 1.25 per sq ft on ceilings.
Leave blank what you don't need. Labour is per area boarded (hang and finish).
Full sheet Cut piece Door or window
How your drywall is worked out
Area to cover, less doors and windows, plus waste ÷ the size of one sheet. Then tape from the joints, compound and screws.
- 1
Area to cover
352 − 36+ ceiling 120= 436 sq ft
- 2
Sheets, +10% waste
347.6 ÷ 32 → 11132 ÷ 32 → 5= 16 sheets
- 3
Tape the joints
186 ft of joints× 1.1 = 204.6 ft= 1 roll of 500 ft
- 4
Compound and screws
436 × 0.14 lb/sq ft= 61 lb → 1 pack552 screws
Read more: the formula, worked examples in feet and metres, typical sizes and tips
Drywall (also called plasterboard, gypsum board or Sheetrock) comes in big sheets. The job is to find the area you will cover, take away doors and windows, add some extra for offcuts and divide by the area of one sheet. Then count the joints between the sheets to know how much tape you need, and use typical figures for compound and screws.
The formula
wall area = 2 × (length + width) × height (whole room), width × height (one wall) or width × height ÷ 2 (gable)
area to cover = wall area − doors × door size − windows × window size (+ length × width for the ceiling)
sheets = area × (1 + waste % ÷ 100) ÷ area of one sheet, rounded up (walls and ceiling apart)
joints on a wall = (rows of sheets − 1) × wall width + (columns − 1) × wall height
tape = (joints + 4 inside corners × height + ceiling joints + room perimeter at the ceiling) × (1 + waste %)
compound = area to cover × compound per area · screws = sheets × screws per sheet
corner bead = corners × whole lengths per corner + window returns ÷ bead length
Worked example
In feet. A room 12 ft long, 10 ft wide and 8 ft high has walls of 2 × (12 + 10) × 8 = 352 sq ft. Take away one 3 × 7 ft door (21 sq ft) and one 3 × 5 ft window (15 sq ft): 352 − 21 − 15 = 316 sq ft. The ceiling is 12 × 10 = 120 sq ft, so the total is 436 sq ft. With 10% waste and 4 × 8 ft sheets (32 sq ft): walls 316 × 1.1 ÷ 32 = 10.86, so 11 sheets; ceiling 120 × 1.1 ÷ 32 = 4.13, so 5 sheets; 16 sheets in all.
Laid across, a 12 ft wall has 2 rows and 2 columns: 1 × 12 + 1 × 8 = 20 ft of joints; a 10 ft wall has 1 × 10 + 1 × 8 = 18 ft. Four walls give 2 × (20 + 18) = 76 ft. Add 4 inside corners × 8 ft = 32 ft, the ceiling joints (3 rows across 12 ft and 2 columns over 10 ft: 2 × 12 + 1 × 10 = 34 ft) and the ceiling edge 2 × (12 + 10) = 44 ft: 186 ft. With 10% extra that is 204.6 ft, so 1 roll of 500 ft. Compound: 436 × 0.14 lb = 61.04 lb, one 62 lb bucket. Screws: 11 × 32 + 5 × 40 = 552, one box of 1,000.
In metres. A room 4 × 3 m and 2.5 m high has walls of 2 × (4 + 3) × 2.5 = 35 m². Take away a 0.8 × 2 m door (1.6 m²) and a 1.2 × 1.2 m window (1.44 m²): 31.96 m², plus a ceiling of 12 m². With 10% waste and 1200 × 2400 mm boards (2.88 m²): walls 31.96 × 1.1 ÷ 2.88 = 12.21, so 13 boards; ceiling 12 × 1.1 ÷ 2.88 = 4.58, so 5 boards; 18 boards. Joints: 38 m on the walls, 10 m of corners, 11 m on the ceiling and 14 m round the ceiling edge = 73 m, × 1.1 = 80.3 m of tape (1 roll of 150 m). Compound: 43.96 m² × 0.7 kg = 30.77 kg, two 20 kg packs. Screws: 13 × 31 + 5 × 39 = 598.
Typical sizes and figures
| Thing | Typical figure |
|---|---|
| Sheets in North America | 4 × 8 ft (32 sq ft), 4 × 10 ft (40 sq ft), 4 × 12 ft (48 sq ft) |
| Boards in metric countries | 1200 × 2400 mm (2.88 m²), 1200 × 2700 mm (3.24 m²), 1200 × 3000 mm (3.6 m²), 900 × 1800 mm (1.62 m²) |
| Ready-mixed joint compound | about 14 lb per 100 sq ft · about 0.7 kg per m² (tape coat plus two coats) |
| Screws | about 1 per sq ft on walls (32 per 4 × 8 sheet), 1.25 per sq ft on ceilings (40 per sheet) |
| Paper joint tape | rolls of 250 or 500 ft · 75 or 150 m |
| Corner bead | 8 or 10 ft lengths · 2.4 or 3 m lengths |
| Door and window | about 3 × 7 ft or 0.8 × 2.0 m · about 3 × 5 ft or 1.2 × 1.2 m |
These are typical trade rules of thumb, checked 11 October 2026. Board makers and local building rules set the real screw spacing, board thickness (for example fire-rated or ceiling boards) and finishing levels, so check them for your job. Joints round doors and windows are covered by the waste figure.
Tips
- Do the ceiling first, then the walls, so the wall sheets hold up the ceiling edges.
- Use the longest sheets you can carry: fewer butt joints means less taping and a flatter finish.
- Keep butt joints away from the corners of doors and windows, where cracks often start.
Common questions
How many sheets of drywall do I need for a room?
Add up the wall area, take away doors and windows, add the ceiling if you are boarding it, then add about 10% for waste and divide by the area of one sheet. A 12 × 10 ft room with 8 ft walls, one door, one window and the ceiling needs 11 sheets of 4 × 8 ft for the walls and 5 for the ceiling: 16 in all.
How much does one sheet of drywall cover?
A 4 × 8 ft sheet covers 32 sq ft, a 4 × 10 ft sheet 40 sq ft and a 4 × 12 ft sheet 48 sq ft. In metric, a 1200 × 2400 mm board covers 2.88 m² and a 1200 × 2700 mm board 3.24 m². Longer sheets mean fewer joints to tape, but they are heavier to lift.
How much joint compound and tape do I need?
A typical figure for ready-mixed compound is about 14 lb per 100 sq ft for taping plus two more coats, or about 0.7 kg per m². For 436 sq ft that is about 61 lb, one 4.5 gallon bucket. Tape is worked out from the joints between sheets, the inside corners and the line where walls meet the ceiling, plus waste.
How many screws do I need per sheet of drywall?
A common rule of thumb is about one screw per square foot on walls, 32 on a 4 × 8 ft sheet, and a few more on ceilings, about 40 on a 4 × 8 ft sheet. For 11 wall sheets and 5 ceiling sheets that is 11 × 32 + 5 × 40 = 552 screws. Follow the spacing your local rules or the board maker give.
Should I hang drywall horizontally or vertically?
Many installers lay sheets across the studs (horizontally) on walls up to about 8 ft, because the long joint sits at a comfortable height and the sheets brace the wall. Upright sheets can give fewer joints on tall walls or narrow spaces. The calculator shows the joint length both ways, and can pick the one with fewer joints.
How much waste should I add for drywall?
About 10% is usual for simple rooms. Use 12–15% for rooms with many doors, windows, corners or sloping ceilings, as more sheets are cut. If you take away nothing for small windows, you can use a lower waste figure, since the cut-outs are already counted.
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